/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.druid.segment.loading;

import org.apache.druid.guice.annotations.ExtensionPoint;
import org.apache.druid.java.util.common.Pair;
import org.apache.druid.java.util.common.logger.Logger;
import org.apache.druid.timeline.DataSegment;
import org.apache.druid.timeline.SegmentId;

import java.util.Map;
import java.util.Set;

/**
 * A DataSegmentFinder is responsible for finding Druid segments underneath a specified directory and optionally updates
 * all descriptor.json files on deep storage with correct loadSpec.
 */
@ExtensionPoint
public interface DataSegmentFinder
{
  Logger log = new Logger(DataSegmentFinder.class);

  /**
   * This method should first recursively look for descriptor.json (partitionNum_descriptor.json for HDFS data storage) underneath
   * workingDirPath and then verify that index.zip (partitionNum_index.zip for HDFS data storage) exists in the same folder.
   * If not, it should throw SegmentLoadingException to let the caller know that descriptor.json exists
   * while index.zip doesn't. If a segment is found and updateDescriptor is set, then this method should update the
   * loadSpec in descriptor.json to reflect the location from where it was found. After the search, this method
   * should return the set of segments that were found.
   *
   * @param workingDirPath   the String representation of the working directory path
   * @param updateDescriptor if true, update loadSpec in descriptor.json if loadSpec's location is different from where
   *                         desciptor.json was found
   *
   * @return a set of segments that were found underneath workingDirPath
   */
  Set<DataSegment> findSegments(String workingDirPath, boolean updateDescriptor) throws SegmentLoadingException;

  /**
   * Adds dataSegment if it does not exist in timestampedSegments. If it exists, replaces entry if segmentModifiedAt is
   * newer than stored timestamp.
   *
   * @param timestampedSegments map of <segmentID, Pair<segment, modifiedAt>> containing segments with modified time
   * @param dataSegment         segment to add
   * @param segmentModifiedAt   segment modified timestamp
   */
  static void putInMapRetainingNewest(
      Map<SegmentId, Pair<DataSegment, Long>> timestampedSegments,
      DataSegment dataSegment,
      long segmentModifiedAt
  )
  {
    timestampedSegments.merge(
        dataSegment.getId(),
        Pair.of(dataSegment, segmentModifiedAt),
        (previous, current) -> {
          log.warn("Multiple copies of segmentId [%s] found, using newest version", current.lhs.getId());
          return previous.rhs > current.rhs ? previous : current;
        }
    );
  }
}
